Process of forming cathode ray tube screens to utilize the luminous efficiency of the phosphor material

ABSTRACT

A PROCESS OF FORMING A CATHODOLUMINESCENT SCREEN OF A CATHODE RAY TUBE WHEREIN THE CHARACTERISTICS OF THE PHOSPHOR MATERIAL, I.E., PARTICLE DENSITY, BULK DENSITY, ATOMIC WEIGHT, ATOMIC NUMBER AND AVERAGE PARTICLE SIZE ARE RELATED IN A MANNER TO PROVIDE A SCREEN HAVING A PRESCRIBED PHOSPHOR WEIGHT AND THICKNESS TO EFFECT EFFICIENT UTILIZATION OF THE LUMINESCENT BRIGHTNESS OF THE RESPECTIVE PHOSPHOR MATERIAL WHEN EXCITED BY SUBSEQUENT ELECTRON BEAM IMPINGEMENT.

Oct 10, R DONOFRK) ETAL 3,697,301

PROCESS OF FORMING CATHODE RAY TUBE SCREENS T UTILIZE THE LUMINOUS EFFICIENCY OF THE PHOSPHCR MATERIAL Filed April 5, 1971 Sheets-Sheet 1 8 67 Z5Kg/ T o loKv Z l0 i E mm ISKV.

u. SHIFT k8 EFFICIENT SCREEN WEIGHT AT 25w '"2/cm INVENTORS.

ROBERT L. DONOFRIO & CHARLES H. REHKOPF ATTORNEY F FORMING CATHODE RAY TUBE SCREENS TO UTILIZE THE LUMINOUS EFFICIENCY OF THE PHOSPHOR MATERIAL Filed April 5, 1971 Sheets-Sheet 5 I 0 I 01 L )1 80 I E 50 I I f w- EA g 40' E m W I a 0 2 4 b 8 IO I2 l4 I6 I8 AVERAGE PARTICLE SIZE (55.55.) MICZONS .30 I00 I r IK/ 1 p a 60 3 u I z E F 3 9 60 BLUE A u 40 F I 5 20 I M (I G k 0 2 4 6 8 IO I2 :4 I6 I8 AVERAGE PARTICLE SIZE. (E555) MICRONS a, n --AI 1.0 m ,4

5 80 I I I E 1 9. 4% m RED i 40 I a: I I 3 20 1 1 I I? 0 2 4 6 l8 :0 I2 14 14. I8 INVENTO AVERAGE PARTI LE sazr: (F.S.S-S)M'C2NS PO6EfiTLwNOliOa CHARLES H. REHKOPF BY CDMTZM ATTORNEY Oct. 10, 1972 DONQFRIO EI'AL 3,697,301

PROCESS OF FORMING CATHODE RAY TUBE SCREENS T0 UTILIZE THE LUMINOUS EFFICIENCY OF THE PHOSPHOR MATERIAL Filed April 5, 1971 5 Sheets-Sheet 4 h-- as 6 Z9'- GREEN 3 4 1 1 51. E B

H] 1 d 2 I 1 u 0') I o i Z 4 6 8 IO l2 l4 I6 I8 AVERAGE PARTICLE SIZE {F.SSS.) MlCRONS f l0 2' I E a r 0 a 6 I! 0 3 3 4 F1 51. B Z a: 1 m z 31 J g o 2 4 e a IOIIZ l4 I618 AVERAGE PARTICLE SIZE (F.s.s.s.) MICRONS I0 35 "V {I 8 1. 1 '---'---7 g 6 z RED 4'8 3 2/ Z 4 z :3 I a: z i U I 0 2 4 e 8 IO '2 I4 16 I8 INVENTORS.

AVERAGE PARTICLE SIZE (F.s.s.s.) MICEONS ROBERT L. DONOFRIO &

BY CHARLES H. REHAOPF ATTOIZNE Y Oct. 10, 1972 DQNQFRIO EI'AL 3,691,301

PROCESS OF FORMING CATHODE RAY TUBE SCREENS TO UTILIZE THE LUMINOUS EFFICIENCY OF THE PHOSPHOR MATERIAL Filed April 5. 1971 5 Sheets-Sheet 6 "OZwOm4 ATTO RN EY United States Patent Ofice 3,697,301 I PROCESS OF FORMING CATHODE RAY TUBE SCREENS T UTILIZE THE LUMINOUS EFFI- CIENCY OF THE PHOSPHOR MATERIAL Robert LtDonolrio, Syracuse, and Charles H. Rehkopf,

Seneca Falls, NiY., assignors to GTE Sylvania Incorporated Continuation-impart of application Ser. No. 846,348, July 31, 1969. This application Apr. 5, 1971, Ser.

No. 130,962 I Int. Cl. Hlllj 31/20 U.S. Cl. 117-33.5 C 11 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 846,348, filed July 31, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to cathodoluminescent screens and more particularly to cathode ray tube screens exhibiting displays of improved brightness.

Cathode ray tubes, especially those adapted for direct visual display applications, conventionally employ at least one electron gun and a related viewing viewing panel having a cathodoluminescent screen of at least one electron responsive phosphor material formed thereon. Dependent upon the intended utilization, the screen can comprise a substantially uniform whiteemitting phosphor combination, a single color-emitting phosphor material, or a discrete pattern of repetitive stripes, bars, or dots of several color-emitting electron responsive phosphor materials.

In the fabrication of white or solid color screens, the phosphor material is usually settled through a liquid cushion, whereas screens for color television utilization are continually formed by a photographic deposition technique wherein a photosensitive polymerizable material is utilized to adhere each of the respective phosphor pattern materials to a substantially transparent substrate oriented relative to the viewing panel. In many instances the substrate is omitted and the screen is formed directly upon the interior surface of the viewing panel per se.

Regardless of the type of screen deposition, an amount of phosphor should be contained therein to achieve a luminous display of desired brightness. Since phosphor materials vary in particle sizes and densities, it is often difficult to arrive at a proper screen weight and particle size to produce a resultant display of desired brightness at a given anode voltage. Extensive experimentation is frequently required to arrive at screen parameters appreaching degrees of operational brightness efiiciencies.

OBJECTS AND SUMMARY OF THE INVENTION It is an obejct of the invention to reduce the aforementioned disadvantages and to provide an improved process for utilizing the inherent brightness efficiencies of the phosphor materials comprising the screen of a cathode 3,697,301 Patented Oct. 10, 1972 ray tube. Another object is to provide a process for prescribing the efficient screen weight and thickness of a phosphor material having a specified average particle size to produce a liuminescent display of desired brightness. A further object is to provide a screen of maximum brightness for a cathode ray tube by a process wherein the screen is optimized relative to specific characteristics of the phosphor material contained therein.

The foregoing objects are achieved in one aspect of the invention by utilizing known characteristics of the respective phosphor materials. Since the phosphor particles of the various electron responsive materials have specific values of particle density (P bulk density (P atomic weight (A), atomic number (Z), and average particle zize (d,,), a screen weight (a) relationship, in mg/cmfi, to effect eificient utilization of the luminescent brightness of the respective phosphor material is expressed as:

screen thickness (11) to provide the efiicient luminescent brightness IS expressed in microns as:

Thus, an expeditious procedure is provided for prescribing etficient screen weight and thicknesses for specific programs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a cathode ray tube;

FIGS. 2, 3 and 4 are charts illustrating the relationship of average particle size, screen weight and percent relative brightness for these specific phosphors;

FIGS. 2a, 2b, 3a, 3b, and 4a, 4b are additional chartings illustrating the relationship of particles size, screen weight, and relative brightness interpolated from the data presented in FIGS. 2, 3, and 4;

FIG. 5 is a chart showing the relationship of particle size-screen weight for several phosphors;

FIG. 6 is an enlarged sectional view showing the relationship of dots in a color screen pattern; and

FIG. 7 is a chart illustrating the effects of a shift in anode voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

With reference to FIG. 1, there is shown a cathode ray tube 11 having an envelope 13 whereof the viewing portion or panel 15 has a cathodoluminescent screen 17 disposed on the interior surface 19 thereof. If desired, the screen 17 can be formed on a separate substantially trans parent substrate, not shown, positioned within the envelop 13 adjacent the viewing panel 15. Oriented within the envelope 13 is at least one electron source 21 positioned to direct at least one electron beam 23 to the phosphor screen 17. Impingement of the electron-responsive phosphor in the screen 17 produces display luminescence 25 of a desired color and brightness.

The screen 17, depending upon the type of display desired, can be of a solid color or of a plural color pattern applied to an area 27 of the viewing panel denoted by the dimension a. Plural color patterns comprising several phosphors are usually formed by photographic deposition whereby the interior surface 19 of the viewing panel has disposed therein a thin film of a photosensitive binder substance, such as sensitized polyvinyl alcohol and a specific color-emitting phosphor material. This coating application can be accomplished by several techniques, for example, one procedure involves first applying a film of the photosensitive substance in the panel 15 and then disposing phosphor powder thereon, while by another method, it may be achieved by the application of a suspension of phosphor in a photosensitive substance. Regardless of how the phosphor is applied, the coated panel is then exposed to light, substantially in the ultraviolet range, to cause the photosensitive substance to light-polymerize and adhere to the interior surface of the panel thus binding the phosphor particles therewith. When forming a patterned screen, as in a color cathode ray tube, the coating comprising a respective phosphor is light exposed by a specifically positioned light source oriented to beam light through an appropriate negative or aperture mask to form a discrete portion of the screen pattern. The exposed screen is then developed to remove the un-polymerized photosensitive substance thereby providing a screen pattern of the respective phosphor. This procedure is repeated for all of the respective phosphors comprising the pattern. In forming a monochrome screen, a settling technique is often utilized wherein the phosphor material is settled through a liquid cushion comprising a silicate binder and water. Usually, formed screens are lacquered, aluminized and then baked to remove the volatile materials introduced during screening and lacquering.

In describing the invention, the screen weight, i.e., the amount of phosphor expressed in milligrams (mg.) per square centimeter (cm. is considered as the weight of the material as screened, and contains a small amount of the respective binder material. For example, in a screen weight of 6.0 mg./cm. the amount of binder present may range from .05 to .16 mg./cm. which is inconsequential to the general results.

Work relating to the invention involved a number of color-emitting phosphors, of which there are green, blue and red illustrated in chart form in FIGS. 2, 3 and 4. To show the relationship between particle size, screen weight and brightness, a representative lot or sample of each of the three phosphor materials was separated into particle distributions according to average sizings of 3, 7, l2 and 16 microns respectively by the Fisher sub-sieve sizer technique (F.S.S.S.). In each case, the F.S.S.S. numher is representative of the average particle size for the respective testing. The individual particle distributions of each phosphor were then made into a number of solid screens of differing screen weights and processed into tubes; whereupon screen brightness measurements were made when the tubes were operated at anode voltages of substantially kv. The data presented in the primary FIGS. 2, 3, and 4 relate to screen brightness vs. screen weight for the several noted average particle distributions. The peaks of the four curves in each figure indicate substantially the maximum brightness conditions for the respective particle distributions. FIGS. 20, 2b, 3a, 3b, and 4a, 4b are additional chartings showing the relationship of particle size, screen weight and relative brightness interpolated from the data presented in primary FIGS. 2, 3. and 4.

Particular reference is made to primary FIG. 2 which illustrates the relative brightness performance of the green-emitting phosphor (Zn Cd ,lSrAg at anode volt ages of 25 kv. Four related curves are presented, whereof the curve r portrays the brightness performance of the 3 micron average distribution which indicates that a maximum reluthe brightness of approximately 86 percent is achieved within a screen weight range of substantially 2.3 to 2.7 mgicnr The curve f shows that the average particle size of 7 microns exhibits a peak brightness of about 94 percent within a screen weight range of substantially 3.8 to 4.6 mg./cm. curve g which represents the average particle distribution of 12 microns has a peak relative brightness of percent within a screen weight range of substantially 5.8 to 6.5 mg./cm. Curve h shows that the average particle distribution of 16 microns exhibits a peak relative brightness of about 92 percent within a screen weight range of substantially 7.7 to 9.0 mg./cm. Also shown in FIG. 2 is a summit brightness curve x which, in joining the peaks of the several curves, indicates that the maximum relative brightness efficiency of this green-emitting phosphor is substantially achieved within a screen weight range of approximately 5.8 to 6.8 mg./cm. wherein the particle size distributions average substantially between about 11 to 13 microns. For additional clarity, reference is directed to FIG. 2a wherein particle size and relative brightness are related in curve 28 which has a. composite slope comprising points e, I, g, and h representing the peaks of curves e, f, g and h respectively in FIG. 2. The curve 28 clearly illustrates that maximum relative brightness efficiency of the particular phosphor material is achieved by utilizing phosphor particles within the size range of substantially 11 to 13 microns. In FIG. 2b curve 29 relates screen weight and particle size wherein points e f g and I: represent the data denoted by peaks e, f, g, and h in FIG. 2. When using a particle size within the range of substantially 11 to 13 microns to realize maximum relative brightness of this specific green phosphor, the op timum screen weight should be within the range of substantially 5.8 to 6.8 mg./cm.

FIG. 3 illustrates the relative brightness performance of the blue-emitting phosphor 'ZnS:Ag at anode voltages of 25 kv. Curves j, k, l, and m indicate substantially the relative brightness peakings of the respective average phosphor particle distributions, and summit brightness curve y denotes that the maximum relative brightness elficiency of this blue-emitting phosphor falls substantially within a screen weight range of approximately 5.0 to 7.0 mg/ cm. wherein the average particle size distributions range substantially between about It to 14 microns. This relationship is further illustrated by curves 30 and 31 in FIGS. 3a and 3b respectively wherein the points j, P k k, l l and m, m are referenced from data points i, k, l, and m in FIG. 3.

A similar charting is presented for the red-emitting YVOpEu phosphor in FIG. 4 wherein curves p, q, r, and s represent substantially the relative brightness peakings of the respective average phosphor particle distributions at anode voltages of 25 kv. The summit brightness curve w shows that the maximum relative brightness efficiency of this red-emitting phosphor occurs substantially within a screen weight range of approximately 4.0 to 6.5 mg./cm. wherein the average particle size distributions range substantially between about 7.0 to 12.0 microns. Further clarification of this relationship is shown in FIG. 4a and 4b wherein curves 32 and 33 are formulated by the respective reference points p q r r, and s, 5*.

FIG. 5 presents particle size'screen weight data for several production lOts of the phosphor materials denoted in FIGS. 2, 3, and 4 along with additional data relative to another green-emitting phosphor, ZnSzCu, and two additional red-emitting phosphors, i.e., Y O :Eu and U20 Eu The plurality of diversely denoted points indicate in1|ximum brightness particle sizescreen weight criteria for the several phosphors considered. It is noted that the data intersection points tend to substantially follmv defined relationships relative to substantially linear gradients 34 extended from 0 on the chart. Substantially avcrage gradients for (Zn Cd )S:Ag. ZnSzCn ZnSzAg, Yv'O zEu, Y O :Eu and (Gd Y O :Eu are denoted as 35, 36, 37, 39, 41 and 43 respectively. To facilitate clarification of FIG. 5, additional data for several representative screen tests of the respective phosphors are presented comprising the screen. Therefore, screen weight is also expressed as:

in Table I. a'==P 'd TABLE I Calculated I Bulk Particle Particle Actual (a) Constant (u) screen density (Pb) size 01,.) Atomic Atomic density screen wt. (K w Phosphor Lot (gm/ernfi) (microns) wt. (A) No. (Z) o) (gm/cm!) values (gmJcmJ) i A g 73 0 2: 53. 2 4. 3 5. 4 0. 0902 6. 9 .06 5 6.2 53.2 4. 3 6.0 0.1000 5. Green Ag c 2. 03 12. a 11s. 24 a3. 2 4. a s. a 0. 0909 6.2 D 1. 99 12. 3 116. 24 53. 2 4. 3 6. 0 0. 1031 5. B G) A 1. 57 8.7 97. 44 46 4. 1 4. 4 0. 0904 4. 8 Green-ZnSzGu B 1. 53 9. 5 97. 44 46 4. 1 4. 8 0. 0899 5. 4 C 1. 54 9. 4 97. 44 46 4. 1 4. 7 0. 0886 5. 3 x 69 3% Iii. g :6 4. 1 5. 4 0. 0945 6. 7 V g g 6 4. 1 6. 00 0. 0 3 Elm-Z113 c 1. 5e 12. 4 97. 44 4a 4.1 1 1 0 1336 2.3 D 1. 52 13. 0 97. 44 4. 1 7. 5 0. 1009 7. 4 o C) 1. 51 8. 0 202. 8 94 4. 34 5. 1 0. 1025 4. 9 Red-YVOuEu 1. 85 7. 5 202. 8 94 4. 34 3. 9 0. 1018 3. 8 1. 60 0. 4 202. 8 94 4. 34 5. 2 0. 0933 5. 5 El 4. 84 4. 0 0. 1257 3. 1 A 7. 4. 8A 4. 7 D. 1116 4. Red YiolsEu c 1. as 6. 6 226 102 4. s4 4. 9 0.1162 4.3 D 1. 62 15. 5 22B 102 4. 84 10. 3 0. 1006 10. 1 I El 1]; if; I; 7. g: 10. 3 0. 1073 9. 3 7. 9. s Red-(GdJY-i 0 1. 4s 7. r ear. 8 152 7. 24 9. s i i 3.3 D 1. 14 5. 9 361. 8 152 7. 24 9. 0 0. 1006 8. 8

With reference to Table I and FIG. 5, it is noted that, in general, the several phosphors appear to have their respective gradients 35 to 43 oriented in a substantially counter-clockwise manner, relative to the o of the chart, substantially in accordance with their particle densities. It further appears that the relationship between particle size and screen weight for the several phosphors tend to deviate from the linear gradients at low and high screen weights and particle sizes. This deviation in linear relationship between phosphor particle size and screen weight is noted in FIG. 5 and also in FIGS. 2b, 3b, and 4b wherein the phosphor materials having a particle density of less than approximately 5.0 show a substantially linear relationship within the particle size range of substantially 8 to 15 microns. The phosphor curves above substantially 15 microns and substantially below 8 microns assume degrees of nonJinearity which have not been established over the full range of particle sizes.

It has been found that a method can be developed to apply to the substantially linear portions of the phosphor relationships by considering the various parameters and characteristics of the respective phosphors to provide a screen having a prescribed phosphor weight and thickness to effect efficient utilization of the luminescent brightness of a particular phosphor material. Particle density (P0), bulk density (P expressed in gm./cm. atomic Weight (A), atomic number (Z) and average particle size (d,,) are combined as follows to denote the approximate calculated optimized screen weight (0') expressed in mg./cm. for a particular phosphor:

The above formulation for determining the functional relationship between particle size and optimized screen weight for a particular phosphor is evolved in the following manner. For example, in its simplest form, a screen of a monolayer approximation is substantially of a single particle thickness (T) having particle density (P The screen weight (0') for this consideration is expressed. as:

o=P -T since it is substantially a monolayer screen its thickness (T) is equal to the particle diameter (d) of the phosphor To calculate the optimized screen weight (a') the particle diameter (d) must be of a value that the energy of the electron beam (e-) incident thereon is most etficiently utilized for excitation of the material. The depth or range of penetration (N) of the incident electron (2*) into the phosphor particle is considered as follows:

Total No. of electrons/ 3 No. of

in screen No. of t Atoms Electrons a 1 :(gms/cm. )-(No. of atoms/gram)-Z No. of atoms/mole Atomic mass/mole k eleot b' z (Wherein k is Avogadros number, a known constant) Since the depth to penetration (N) is proportional to 1 elee! a lent h' then Therefore, the functional relationship between the optimum or calculated screen weight (a') is expressible as a restricted linear approximation:

A ZP

The constant K is empirically determined and includes the aforementioned Avogadros number k. When actual or known values of eflicient screen weight (a) are utilized, K represents an average slope of phosphor data and is expressed as:

While a K" value range of substantially 0.07 to 0.18 is found to be workable, a preferred range is between substantially 0.07 and 0.13. For phosphors having particle densities ranging substantially between 4.0 and 7.5, an average K value of approximately 0.099 has been found appropriate. As referenced per curve 43 in FIG. and the representative data in Table I, it is noted that phosphors having particle densities above the 5.0 value appear to fulfill the linear conditions of the equation.

Since the luminescent brightness efiiciency of the screen per se is related to screen thickness, the eflicient thickness of the screen (it) to achieve maximum brightness for a particular phosphor having a known particle size distribution is expressed in microns as: P,, b

While the foregoing examples of eflicient screen weights and thicknesses have been concerned with solid screens, the same holds true for a patterned multi-phosphor color screen as each portion of the color pattern is first disposed as a continuous solid layer. Since patterned color screens are conventionally formed by photo-deposition techniques, the applied continuous layer of phosphor and appropriate binder is exposed and developed to form a discrete portion of the pattern. The other phosphors comprising the pattern are subsequently disposed in like manner. An enlarged portion of a color screen pattern is shown in FIG. 6 wherein cross-sectional views of three phosphor dots 57, 59 and 61, which for example are formed of blue, red and green-emitting phosphors respectively and are representations of a vast multitude of dots comprising the screen patterns. These dots which have been formed on the tube viewing panel or substrate by photodeposition are the residuals of three separate layer-type applications of phosphor and binder, each of which had a screen weight and thickness calculated as aforedescribed. For example, the blue dot 57 of ZnS:Ag material has an average particle size (d,,) of substantially 11.5 microns, a calculated screen weight (a) of substantially 6.8 rug/cm? and a screen thickness (11,) of substantially 32.0 microns. The red dot 59 for example being of YVOgEu phosphor has an average particle size (d,,) substantially of 9.4 microns, a calculated screen weight (0") of substantially 5.5 mg./ cm, and a screen thickness (n of substantially 25.5 microns; while the green dot 61, for example, is of ZnCdS Ag material having an average particle size ((1,) of substantially 12.5 microns, a calculated screen weight (a') of substantially 5.9 mg./cm. and a screen thickness (n,,) of substantially 27.4 microns. In this color screen, for example, the phosphors in the multi-dot pattern occupy approximately equal portions of the screen area comprising about 95 percent of the total screen area, the remaining approximate 5 percent being interstitial spacing. Thus, the screen weight of the pattern would be substantially 95 percent of the average (6.07 mgJcm?) of the three calculated screen weights, which in this instance is 5.77 rug/cm It has been mentioned that the foregoing calculated efficient screen weights are related to substantially 25 kv. anode operation. As shown in FIG. 5, the average phosphor particle size distribution range for each material includes the linear portions of the respective phosphor curves 35 to 41 which relate to the average phosphor particle size distribution range extending substantially between 8 and 15 microns and screen weights falling substantially between 4.5 and 8 mgJcmF. In referring to FIG. 7, there are shown two anode voltage shift curves, i.e.. the 25 kv. to 18 kv. shift 65 and the 25 kv. to 10 kv. shift 67. Voltage shift curve 65 shows that for the concerned screen weights ranging between substantially 4.5 and 8.0 ing/cm. there is an approximate 6.0 percent decrease in screen weight at the 4.5 mg. level and practically none at the 8.0 mg./cm. level. Thus, for the reduction in anode voltage to 18 kv. there is less than .25 rug/cm. change in screen weight. In referring to the voltage shift curve 67 there is shown an approximate 8.5 percent decrease in screen weight at the 4.5 mgjcm? level and about a 3.5 percent reduction at the 8.0 ing/cm. level. The resultant weight reductions range from about .38 mg./cm. down to .28 ing/cm Since deviations of .5 mg./cm. or less are considered to be within the accepted tolerance of the screen weight calculations, herein considered, the above-noted screen weight reductions are not considered significant. In general, it has been found that screens having phosphor weights in substantially the 4.5 to 8.0 mg./ cm. range do not require an appreciable altering of screen weight for reductions in anode voltages from substantially 25 to 10 kv.

It has been shown from the data herein presented that there is close correlation between the calculated eflicient screen weights and the actual eflicient screen weights for a plurality of phosphor materials.

Thus by this improved method, it is feasible to substantially calculate the eificient screen weight, elficient screen thickness and optimum particle size for a number of phosphor materials having particle densities less than 5.1 and average particle sizes falling within the range of substantially 8 to 15 microns.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An improvement in the process of forming the cathodoluminescent screen of a cathode ray tube on a suitable substrate wherein the phosphor particles have specific values of particle density (P bulk density (P expressed in g./cm. atomic weight (A), atomic number (Z), and average particle size (d,,) to provide a screen thickness (n) of related phosphor material weight (0") to effect efficient utilization of the luminescent brightness of the respective phosphor material when excited by subsequent electron beam impingement, said improvement comprising:

disposing on said substrate a binder substance and at least one electron excitable phosphor material having an average particle size of less than 15 microns, whereof the screen formed of said phosphor material has an approximate calculated screen weight (0) expressed in mg/cm. as:

wherein K is an empirically determined constant representing an average slope of phosphor data, utilizing a known screen weight value expressed in terms of:

U K: an

said value of K ranging substantially from 0.07 to 0.18.

2. An improvement in the process of forming a cathodoluminescent screen of a cathode ray tube according to claim 1 wherein the value of constant K is preferably within the range of substatnially 0.07 to 0.13.

3. An improvement in the process of forming a cathodoluminescent screen of a cathode ray tube according to claim 1 wherein the constant K has an approximate average value of substantially 0.099.

4. An improvement in the process of forming the cathodoluminescent screen of a cathode ray tube according to claim 1 wherein the screen thickness (n) is expressed in microns as:

5. The improved process according to claim 1 wherein the relationship between phosphor particle size and screen Weight for phosphor materials having a particle density of less than 5.0 is substantially linear within the particle size range of substantially 8 to 15 microns.

6. An improved cathodoluminescent screen for a cathode ray tube disposed on a substantially transparent substrate whereof the phosphor particles in said screen have specific values of particle density (P bulk density (P expressed in g./cm. atomic weight (A), atomic number (Z), and average particle size (d,,) to provide a screen thickness (n) of related phosphor material weight (0') to effect efiicient utilization of the luminescent brightness of the respective phosphor material when excited by electron beam impingement, said screen comprising:

at least one electron excitable phosphor material disposed on said substrate and having an average particle size of less than 15 microns, said phosphor deposition having an approximate calculated screen weight (6') expressed in mg./cm. as:

wherein K is an empirically determined constant representing an average slope of phosphor data, utilizing a known screen weight value (0), expressed in terms 7. An improved cathodoluminescent screen for a cathode ray tube according to claim 6 wherein the value of said constant K" is preferably within the range of substantially 0.07 to 0.13.

8. An improved cathodoluminescent screen for a cathode ray tube according to claim 6 wherein said constant K is substantially 0.099.

9. An improved cathodoluminescent screen for a cathode ray tube according to claim 6 wherein the thickness (:1) of said screen is expressed in microns as:

10. An improved cathodoluminescent screen for a cathode ray tube according to claim 6 wherein the relationship between phosphor particle size and screen weight for phosphor materials having a particle density of less than 5.0 is substantially linear within the particle size range of substantially 8 to 15 microns.

11. An improved cathodoluminescent screen for a color cathode ray tube according to claim 6 wherein said screen comprises a pattern array of at least two different phosphor materials exhibiting compatible hues; and wherein the calculated screen weight of each phosphor is separately determined by said formulation as a solid screen consideration prior to the formation of the respective pattern elements of said phosphor.

References Cited UNITED STATES PATENTS 3,460,962 8/1969 Thornton 1l7--33.5 CM 3,481,733 12/1962 Evans 1l733.5 C X 3,573,084 3/1971 Gallaro 313-92 R X RALPH S. KENDALL, Primary Examiner C. WESTON, Assistant Examiner US. Cl. X.R.

ll733.5 CM; 31392 R, 92 PD mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 Dated October 10, 1972 Inventor) Robert L. Donofrio and Charles H. Rehkopf It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Table I Column Heading No. 8 should read:

Actual o" Screen Wt. (mg. /cm.

Table I Column Heading N0. 10 should read:

"Calculated 0") Screen Wt. (mg. /cm.

Signed and sealed this 13th. day of March 1973.

(SEAL) Attest EDWARD M FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

